Fuzz Face

This is the Fuzz Face, the legendary fuzz distortion pedal. With this PCB you can build the original or many other variants using either Germanium or Silicon transistors.
Steps

Created by DHEA
Status: Active
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Designators and components Step 2 of 4

NEGATIVE OR POSITIVE GROUND

The PCB is designed for the original positive ground version (PNP transistors). A positive ground pedal cannot be connected to the power supply in chain with your other pedals (negative ground).  It is necessary to use a 9V battery, an isolated power supply or a voltage inverter.

If you are planning about using germanium transistors, you should build the positive ground version because most of the germanium transistors are PNP (AC128 for example). You can also compare several PNP germanium transistors or even use PNP silicon ones. However, if you are going to use only silicon transistors, you should build the NPN version... which will be more convenient to power up in chain with your other pedals.

To convert to the negative ground version (NPN transistors) is simple: change to NPN transistors, flip the polarity of the electrolytic capacitors (C1, C2 and C4) and connect the +9V where it is marked -9V.

Capacitors for PNP version                 Capacitors for NPN version

COMPONENTS LIST

Version 1

Version 2 (from Jan 2017)

TRANSISTORS

The original Fuzz Face employs germanium transistors (AC128 or NKT275); however it may be a little difficult to get some decent units nowadays. You can buy them already matched on Ebay or online stores. If you have a batch of transistors, you should use a low gain in the first stage (β=70-80) and a high gain in the second stage (β=110-130). Germanium transistors tend to have leakage current and a varying gain value.

For the PNP silicon version you can use 2N3906. For NPN silicon version you can use 2N3904BC108 or BC109. You can also use sockets and try different transistor combinations. Note that each transistor has different gain characterics.

For the correct position of the transistors you can use the following figures.

In the following table find some transistors you can use. 

TRANSISTOR SOCKETS

It is recomended to use sockets for the transistors. You can easily use individual pin headers (40 PIN DIP SIP IC SOCKETS ADAPTOR SOLDER TYPE) or  TO-5 sockets.

 

 

BIASING THE CIRCUIT

You can use the trimmer to bias the circuit. By using a voltmeter, you can measure the voltage over the "Bias" pad and adjust to half of the power supply. For example, if you are using a 9V power supply, you should bias it at 4.5V. Note that if you are using germanium transistors the biasing will easily be influenced by ambient conditions such as temperature. Other method is just using your ears, rotate the trimmer until you find the position you most like.

 

GENERAL DESCRIPTION OF COMPONENTS

Resistors
The resistors are ¼ Watt metal type. You can either use a multimeter or the color bands to obtain their values. Resistors don’t have polarity; you can assemble them in any direction.

Electrolytic capacitors
Electrolytic capacitors have the value printed on them. The polarity is also is marked for the negative lead, additionally the longer leg is the positive and shorter the negative. Assemble the electrolytic capacitor according with the positive polarity (+) marked in the PCB, that is, the longer leg of the capacitor is passed through the pad marked with +.

Polyester capacitors
The polyester capacitors have three numbers, read as picofarads (pF), the first two are the 1st and 2nd digits and the third is the multiplier code. This type of capacitors doesn’t have polarity; you can assemble them in any direction.

Ceramic capacitors

The ceramic capacitors have three numbers, read as picofarads (pF), the first two are the 1st and 2nd digits and the third is the multiplier code. This type of capacitors doesn’t have polarity; you can assemble them in any direction.

Potentiometer
Potentiometers can be mounted directly on the PCB. For a correct orientation, the potentiometer shaft is marked on the PCB.